1. Field of the Invention
This invention relates to ionizers, which are designed to remove or minimize static charge accumulation. Ionizers remove static charge by generating air ions and delivering those ions to a charged target. This invention uses a collimator in combination with ionizer fans to improve the effectiveness of ion delivery to the target.
2. Description of Related Art
Ionizers remove static charge by ionizing air molecules, and delivering those generated air ions to a charged target. The air ions are typically created by high voltage applied to emitter tips, by nuclear disintegration, or by ionizing radiation. The location wherein the air ions are created is referred to as the source of air ions. Positive air ions neutralize negative static charges, and negative air ions neutralize positive static charges. Delivering the ions to the target is a major factor in overall ionizer effectiveness since air ions are lost during the transport time. Air ion losses explain why static charge removal may occur in a fraction of a second at close distances from the ionizer, yet require 30 seconds at large distances. There are two primary mechanisms responsible for air ion loss: recombination and grounding.
Recombination occurs when positive air ions collide with negative air ions. The products are two neutral air molecules that have no capability to remove static charge. Recombination is a function of air ion density and transport time. Higher air ion density increases the recombination rate, and more transport time increases the period over which that recombination rate operates.
Grounding occurs when ions contact a grounded surface. This happens when ions are delivered into a large area containing a small target of interest. Only those air ions directed to the small target are useful. Those air ions delivered outside the target circumference miss the target, and are eventually grounded. Hence, they performed no useful work.
A partial solution to reduce recombination and grounding is to employ fans in the ionizer. This solution is prior art, and commercial products are available. The fan provides a stream of fast moving air that carries the ions toward the target. Recombination is reduced because ions are diluted into the airflow of the fan. That is, air ion density is reduced by additional air, and reduced air ion density leads to a lower recombination rate. Also, transport time is reduced because the air ions are blown toward the target by the fan's average velocity.
However, fans by themselves miss the opportunity for even better ionizer performance. Without modification, fans introduce problems that limit the available benefit.
For example, fans produce turbulent air, not smooth laminar air. Turbulent air creates mixing, and mixing increases the rate of recombination. It is a generally known principle of chemistry that mixing or stirring increases the speed of reaction. More ions would be available for static charge removal if the turbulence could be reduced.
Ionizers with fans also produce a wide conical profile of ions moving toward the target. Hence, many of the generated ions are blown outside the target, and are eventually grounded. In essence, these ions are wasted.
Unmodified fans do not make use of inherent high velocity zones. Fan blades create the highest velocity in the outer ⅓ of the fan's radius. Fan blades are typically wider at the circumference than at the motor hub connection. So, there is more surface area imparting momentum to the air. The outside of the blade also moves faster than the inside. Again, more momentum is supplied to the air from the outside of the blade. If air ions could be maintained in the high flow zones, they would move faster toward the target, and air ion recombination would be minimized. Unfortunately, the high flow zones in unmodified fans quickly degenerate into turbulence. Also, these high flow zones tend to blow ions outward rather than straight at the target.
If the fan's high velocity zone is maintained, air entrainment occurs. Bernoulli's model describes this phenomenon. Fast moving air has lower pressure than surrounding still air. So, the still air of the environment is pulled into the fast moving air. More air means more dilution of the ions. As the density of the air ions decreases, recombination decreases. As noted previously, unmodified fans do not maintain a high velocity zone.
Fans without modification do not provide a mechanism to delay the mixing of positive and negative ions. Fans possess no barriers that can briefly separate positive and negative ions. Yet the ability to briefly separate positive and negative ions is known to decrease recombination loses. This fact is evident from the behavior of pulsed DC ionizers. Low pulse frequencies deliver more useful ions to the target than high pulse frequencies because mixing is delayed.